The invention comprises a method and apparatus for imaging both external and internal characteristics of standing tree stems, or felled stems logs, or wood pieces including hidden internal features such as the presence and position of knots or whorls which are not necessarily externally visible, resin pockets, internal checks, annual growth rings, sapwood and heartwood or sapwood-heartwood transitions, earlywood and latewood, and the depth of the clearwood sheath in a pruned stem or logs or from a pruned stem.
In New Zealand commercially grown Pinus radiata are often pruned of branches at a number of intervals over the 25 to 30 year typical growth period between planting and harvesting. This is also the case for southern pine species in the USA. Such pruning may result in a defect core, including knots, becoming hidden within the tree stem as a tree continues to grow and subsequent growth rings cover the branch stub end, or more commonly where a number of branches have been pruned at the same height on the stem a whorl of knots remains within the tree stem, which again may commonly become hidden as the tree continues to grow. Knots or whorls and other internal characteristics such as resin pockets or internal checks (voids) are considered defects within the wood. They typically render the wood unsuitable for higher value wood applications and are structural weaknesses such that timber pieces including such defects may be unsuitable for structural applications. The zone of wood formed outside the defect core is known as the clearwood sheath and typically contains high value, defect free wood. The presence of such hidden internal defects and the volume of clearwood is general not known until after the logs have been sawn, when the presence of internal defects is revealed. There are currently no known practical, accurate and reliable methods for predicting in detail the quality and potential value of the wood within mature standing tree stems especially pruned stems. The currently most accurate prediction methods require felling a sample of the mature trees and either destructively analysing the sample in the forest, or processing them and intensively studying the resulting products.
In general tree stems are assessed by visual assessment and measurement of externally visible characteristics by skilled workers as to the apparent optimum cutting points for bucking the tree stems into logs. Similarly, stems or logs are commonly visually assessed for suitability of the wood for a particular end use, such as structural or other solid wood applications, veneer production, or pulp and paper production.
There are a number of patents in the prior art which disclose the scanning of sawn timber with radar or microwave frequency radiation in systems for detecting the presence of knots on the surface of the sawn timber, such as U.S. Pat. Nos. 4,607,212, 4,500,835, and 4,123,702, and UK patent 1,489,554 for example.
In broad terms in one aspect the invention comprises a method for assessing standing tree stems, or for determining cutting points for processing of felled tree stems, logs or other wood pieces, or for assessing stems, logs, or wood pieces for end use, comprising scanning a stem, log or piece with shortwave or microwave electromagnetic energy, detecting the energy reflected from the wood, processing the resulting scan data to produce an image indicating hidden internal characteristics and their position within the stem, log, or piece, and assessing the image together with information to the external shape or dimensions of the stem, log, or piece and identifying cutting points for the stem, log, or piece or allocating the stem, log, or piece or part of parts thereof to an end use.
Preferably information as to the external shape and dimensions of the stem, log, or piece and the depth of detected internal characteristics is all obtained from the scan data.
Preferably the method includes determining the depth of the clearwood sheath from the surface of the wood for a pruned stem.
In broad terms in another aspect the invention comprises apparatus for assessing standing tree stems, or for determining cutting points for processing of felled tree stems, logs or other wood pieces, or for assessing stems, logs, or wood pieces for end use, comprising scanning means arranged to scan the stems, logs, or pieces with shortwave or microwave electromagnetic energy and to detect the energy reflected from the wood, associated computer processing means arranged to process the resulting scan data as to internal characteristics of the stem, log, or piece together with information as to the external shape or dimensions of the stem, log, or piece and produce an image of both the external shape and indicating hidden internal characteristics and their position and the depth of clear wood within each stem, log, or piece.
The electromagnetic energy may be radar frequency energy or microwave frequency energy. A preferred frequency is in the range 0.5 to 20 GHz, more preferably 5 to 10 GHz, and most preferably about 8 GHz.
The method and apparatus of the invention are directed to both the detection of hidden defects such as knots or whorls or other defects within the stems, logs or wood pieces, which are not readily visually apparent from the exterior. This may be by assessment of stems of standing trees before felling to determine their readiness for harvesting, or by assessment of felled stems before bucking into logs or before sawing of logs into timber pieces in a sawmill or peeling of bolts in a veneer plant, to obtain the optimum cutting points. The cutting point or end use may be determined taking into account the depth of clearwood and presence of hidden defects, and to maximise the economic value obtained from the harvested trees. In addition the invention involves producing an image showing the internal hidden characteristics and preferably in addition the external shape of the stem or log or wood piece, and assessing the image to identify the optimum cutting points for or to allocate the stem, log or wood piece or parts of it to a particular end use such as sending of the log to a sawmill for processing to structural or finishing grade timber or to a veneer plant, or sending of the log for chipping for pulp and paper production for example. Preferably the external shape and dimensions of the stem or log or wood piece are obtained from the scanned data but alternatively information as to the external shape and/or dimensions of the stem or log or wood piece may be obtained by other means such as an electronic measuring device or system or a scanning system using another technology. The resulting image of the stem or log may be displayed to and assessed by an operator on a screen, or alternatively may be an image in electronic form which is further processed by software to identify the optimum cutting points or optimum end use for the stem or log or parts thereof with the resulting information being displayed to an operator, printed on a tag which is attached to the stem or log comprising information as to optimum cutting points or end use, or passed to the control system of a further online processing stage involving automated cutting of stems into logs or logs into timber pieces, or allocation or redirection of logs for solid wood or pulp and paper end use.